Multilayered structures which are both substantially impervious to gases and/or moisture are well known in the medical and food packaging industries. However, current structures suffer from a variety of problems, including environmental incompatibility, rapid deterioration after exposure to sterilizing radiation, lack of toughness, ineffective heat sealability, and an embarrassing tendency for personal care articles manufactured from these structures, such as ostomy pouches, to make noise due to wrinkling during use.
Currently, poly(vinylidine chloride) (PVDC) is used as one of the materials of choice for the gas barrier component of barrier films. For ostomy applications, a film of PVDC sandwiched between opposing layers of low density polyethylene (LDPE) is widely used, with PVDC functioning as the gas barrier, and LDPE as the moisture barrier. Also, polyvinyl chloride (PVC) can be used in the moisture barrier layer, or other layers, of such a structure. However, disposal of these chlorine-containing materials presents a number of environmental concerns, especially relating to incineration of these materials after use in hospitals or otherwise.
Both PVDC and PVC are viewed as hazardous to the environment and to personal health. Incineration of PVDC/PVC results in release of hydrochloric acid (HCl), providing the major portion of HCl in incinerator flue gases. Also, PVDC/PVC is suspected of contributing to polychlorinated dibenzodioxin and furan toxins formed during incineration. Levels of these toxins are up to three times greater in medical infectious waste as compared to municipal waste streams. See e.g., Staff Report, "Proposed Dioxius Control Measure for Medical Waste Incinerators", State of California, Air Resources Board, Stationary Source Division, pp. 1-40 (May 25, 1990); Medical Waste Policy Committee, "Perspectives on Medical Waste", A Report of the Nelson A Rockefeller Institute of Government, State University of New York (June, 1989). In addition to incineration concerns, exposure to di-2-ethylhexylphthalate (DEHP), a common plasticizer utilized with PVDC and PVC, may present a number of health-related concerns, including reduced blood platelet efficacy, and potential links to liver cancer. See e.g., Allwood, M. C., "The Release of phthalate ester plasticizer from intravenous administration sets into fat emulsion", 29 International Journal of Pharmacology, 233-6 (1986).
Examples of barrier structures incorporating such hazardous chlorine-containing materials can be found in various U.S. Patents, such as U.S. Pat. No. 3,524,795, which discloses a layered packaging material with a gas barrier layer comprised of various vinyl chlorine-containing polymers, and U.S. Pat. No. 4,786,561, which discloses a heat-shrinkable barrier film of an oriented polyolefin film coated on one side with a vinylidene chloride copolymer. In addition, numerous other patent documents, including U.S. Pat. Nos. 5,009,648, 4,983,171, 4,906,495, 4,880,592, 4,826,493; British Patent Application No. GB 2138431; and European Patent Application No. EP 0433060; all disclose multilayered films which utilize chlorine-containing polymers for the construction of ostomy pouches and other personal care articles.
Crystalline polypropylene provides excellent protection from moisture and is often a material of choice for barrier structures, and for medical articles manufactured therefrom. In addition, crystalline polypropylene exhibits a number of other desirable properties, such as non-toxicity, chemical resistance and inertness to drugs and liquid media used with drugs, as well as its low cost and ease of processing by means of extrusion, molding, and the like. However, a disadvantage of crystalline polypropylene is its inherent inability to be heat sealed to other materials. Thus, medical articles, such as barrier structures, or packaging for medical articles, often cannot be effectively heat-sealed in the manufacture and/or assembly of the components of the article. Furthermore, similar problems may also occur in the packaging of pharmaceuticals or medical articles in an effort to protect them from undesired exposure to environmental contaminants, including pathogenic organisms.
Even after manufacture and assembly, such barrier structures and/or medical articles often require additional protection beyond secure heat sealing and package processing. Accordingly, such materials should be sterilized at the time of production, and thereafter maintained in a sterile condition during storage. While not all structures or articles require sterilization prior to usage, structural components which are resistant to radiation are more versatile for uses in medical articles and packaging than components unable to maintain structural integrity after irradiation. Thus, the most desirable material for a barrier structure, medical article, or the packaging formed therefrom, is one which possesses resistance to the structurally demanding forms of sterilization, such as by gamma or electron-beam radiation, even if current usages of the structure or articles do not require such sterilization.
A preferred method of sterilization uses gamma radiation, such as radioactive cobalt 60, since it can be performed on packages sealed by heat or other methods, insuring total and reliable sterility of the contents. In addition, electron beam radiation can also be utilized to sterilize barrier structures, medical articles, and/or their packaging materials.
Unfortunately, a further disadvantage of crystalline polypropylene is that gamma-irradiation or electron-beam irradiation causes degradation of its structural integrity (e.g., causing embrittlement, discoloration, and thermal sensitivity). Thus, barrier films incorporating crystalline polypropylene in moisture barrier layers, or other layers, and the articles or packaging materials formed therefrom, are incapable of maintaining their structural integrity for a useful period of time after exposure to ionizing radiation.
Examples of barrier structures and/or the articles formed from these structures which incorporate crystalline polypropylene are shown in numerous U.S. and foreign patents, including U.S. Pat. Nos. 4,217,161 and 4,511,610, which disclose multilayered plastic vessels or containers, and processes for making such containers. The films comprising these vessels or containers include an inner gas barrier layer and outer moisture barrier layers of a crystalline polyolefin, preferably crystalline polypropylene or crystalline polypropylene/ethylene copolymers.
U.S. Pat. Nos. 4,239,826 and 4,254,169, both disclose multi-layer barrier films with a core gas barrier layer of a vinyl alcohol polymer or copolymer between opposing layers of a polyolefin blended with a chemically-modified polyolefin containing functional groups added thereto. Examples of chemically-modified polyolefins include vinyl acetate-vinyl alcohol copolymers, vinyl alcohol-ethylene vinyl acetate terpolymers, or high density polyethylene with an unsaturated fused-ring carboxylic acid grafted thereto. In addition, the films can contain additional outer layers overlying the modified polyolefin layers of polyolefin polymers or copolymers, such as high, medium and low density polyethylene, polypropylene, ethylene vinyl acetate copolymers, ethylene acrylic acid copolymers, nylons, or blends thereof.
Other exemplary patents include, Japanese Patent Application No. Sho 60[1085]-217190, published Apr. 6, 1987, which discloses a plastic laminate comprised of a polyvinyl alcohol gas barrier layer, with a plastic, olefin-containing, vapor barrier layer laminated thereto. Also, U.S. Pat. No. 4,064,296 discloses a heat shrinkable, multilayer film having a gas barrier layer and outer moisture barrier layers of oriented olefin polymers, which have been crosslinked through exposure to ionizing radiation. In addition, U.S. Pat. No. 4,407,897 discloses a multi-layer polymeric structure with a drying agent incorporated therein, and with outer moisture barrier layers of polymers such as polyethylene, polypropylene, or blends thereof.
Attempts have been made to overcome degradation problems associated with crystalline polypropylene. For example, mesomorphous polypropylene, as described in U.S. Pat. No. 4,931,230, and articles manufactured from mesomorphous polypropylene, such as described in U.S. Pat. No. 4,950,549, provide resistance to sterilizing irradiation. By controlling the method of preparing mesomorphous polypropylene, through the quenching of such polypropylene after hot-melt extrusion, the material or articles formed therefrom substantially maintain their structural integrity after exposure to ionizing radiation at dosages sufficient to degrade crystalline polypropylene.
Unfortunately, single-layer packaging films and the like made from crystalline polypropylene, or even mesomorphous polypropylene, are susceptible to tearing and puncturing which would disrupt the structural integrity of a manufactured component or packaging film after assembly. Thus, the usefulness of a sterilized medical article would be compromised by a puncture or tear in a polypropylene package. In addition, single-layer crystalline polypropylene cannot be effectively heat sealed against another material. Furthermore, even though mesomorphous polypropylene provides better heat sealability than crystalline polypropylene, in certain instances it still cannot provide a sufficient heat seal to manufacture a multicomponent medical article, or to provide an effective radiation-sterilized package.
In an effort to overcome these deficiencies, polymer blends of mesomorphous polypropylene and a polymer compatible with such polypropylene, as described in European Patent Application No. 0 405 793 (assigned to the same assignee as for this application) have been developed. These polymer blends exhibit enhanced physical properties, such as heat sealability and tear strength, while maintaining the radiation resistance associated with mesomorphous polypropylene.
Though mesomorphous polypropylene, or blends thereof, may be radiation resistant, the materials comprising the gas barrier layer of barrier films typically are not. For example, as described in Evalca Technical Bulletin No. 140 (available from Evalca Co., of EVAL America, located in Lyle, Ill.), typical gas barrier polymers, such as ethylene vinyl alcohol (EVOH) rapidly degrade after exposure to ionizing radiation. Furthermore, the polymeric adhesive layers often employed in such barrier films would also be expected to rapidly degrade after exposure to ionizing radiation.
To date, no barrier film exists which combines radiation resistance with environmental compatibility. Furthermore, there are no such barrier films which likewise exhibit one or more good packaging or component article properties, such as heat sealability, toughness, softness, and quietness.